It's possible that you're feeling the missmatch between the timing and the AFR.
If you can get a bit more advance at that rpm I think it would help.
But also agree it seems lean for the conditions based on the WBO2
Sidenote - Not sure I entirely believe it (the WBO2) since you observed fuel burning in the exhaust. The WBO2 interpretation to AFR depends on the burn being within the expected norms....
MAB can effect start up of the mains, but I'd want to know what and where the emulsion bleeds are first.